[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 150241
TCDAT2

Tropical Storm Fiona Discussion Number   3
NWS National Hurricane Center Miami FL       AL072022
1100 PM AST Wed Sep 14 2022

Although the system still appears ragged-looking in satellite
images, a very recent ASCAT-B pass indicated that the tropical
cyclone has strengthened.  Maximum winds in the pass were around 45
kt and therefore, the initial intensity has been increased to that
value. It should be noted that Fiona is an asymmetric storm with all
of its thunderstorms and strong winds currently located on the
system's east side.  The lopsided structure is due to moderate
west-southwesterly vertical wind shear.

Fiona continues to move westward at 12 kt. The steering pattern
seems relatively straightforward.  A low- to mid-level subtropical
ridge situated over the central Atlantic should steer the system
westward to west-northwestward during the next several days, taking
the cyclone across the northern Leeward Islands by Friday night,
near the Virgin Islands and Puerto Rico on Saturday, and near
Hispaniola on Sunday and Monday.  There will likely be a turn to the
northwest by the end of the period when the system reaches the
western periphery of the ridge.  The models all show a similar
theme, but there are notable speed differences with the ECMWF model
faster than the remainder of the guidance.  The NHC track forecast
is quite similar to the previous one and near a consensus of the GFS
and ECMWF models.

Given the current tilted and asymmetric structure, continued
influences of shear, and some dry air, any strengthening of the
storm will likely be slow to occur during the next day or so.
However, some of the models show Fiona moving into a less hostile
environment in a couple of days, and it could have an opportunity to
become a little stronger this weekend if it avoids the landmasses of
Puerto Rico and Hispaniola.  Given the uncertainty of the system's
future environment and potential land interaction, little change in
strength is shown through most of the period. However, it should be
noted that the intensity forecast is of low confidence given those
complexities.

Key Messages:

1. Tropical storm conditions are possible in portions of the
northern Leeward Islands by Friday night, where a Tropical Storm
Watch has been issued.

2. Heavy rains will begin to affect the northern Leeward Islands
late Friday, spreading into the British and U.S. Virgin Islands and
Puerto Rico over the weekend. This rainfall may produce isolated
flash and urban flooding, along with isolated mudslides in areas of
higher terrain.

3. Fiona is expected to move near the Virgin Islands, Puerto Rico,
and Hispaniola this weekend and early next week, and Tropical Storm
Watches will likely be issued for some of those areas on Thursday.


FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 16.7N  52.0W   45 KT  50 MPH
 12H  15/1200Z 16.9N  53.8W   45 KT  50 MPH
 24H  16/0000Z 17.1N  56.3W   50 KT  60 MPH
 36H  16/1200Z 17.2N  58.9W   50 KT  60 MPH
 48H  17/0000Z 17.3N  61.5W   50 KT  60 MPH
 60H  17/1200Z 17.6N  63.8W   50 KT  60 MPH
 72H  18/0000Z 17.8N  65.8W   50 KT  60 MPH
 96H  19/0000Z 18.7N  68.6W   50 KT  60 MPH...INLAND
120H  20/0000Z 20.5N  70.6W   50 KT  60 MPH

$$
Forecaster Cangialosi
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